The present invention relates generally to chemical mechanical polishing of substrates, and more particularly to polishing with fixed-abrasive polishing pads.
Integrated circuits are typically formed on substrates, particularly silicon wafers, by the sequential deposition of conductive, semiconductive or insulative layers. After each layer is deposited, the layer is etched to create circuitry features. As a series of layers are sequentially deposited and etched, the outer or uppermost surface of the substrate, i.e., the exposed surface of the substrate, becomes increasingly non-planar. This non-planar outer surface presents a problem for the integrated circuit manufacturer. Therefore, there is a need to periodically planarize the substrate surface to provide a relatively flat surface. However, in some fabrication processes, planarization of the outer layer should not expose underlying layers.
Chemical mechanical polishing (CMP) is one accepted method of planarization. This planarization method typically requires that the substrate be mounted on a carrier or polishing head. The exposed surface of the substrate is placed against a rotating polishing pad. The polishing pad may be either a xe2x80x9cstandardxe2x80x9d pad or a fixed-abrasive pad. A fixed-abrasive pad has abrasive particles held in a containment media, whereas a standard pad has a durable surface, without embedded abrasive particles. The carrier head provides a controllable load, i.e., pressure, on the substrate to push it against the polishing pad. A polishing slurry, including at least one chemically-reactive agent, and abrasive particles if a standard pad is used, is supplied to the surface of the polishing pad.
An effective CMP process not only provides a high polishing rate, but also provides a substrate surface which is finished (lacks small-scale roughness) and flat (lacks large-scale topography). The polishing rate, finish and flatness are determined by the pad and slurry combination, the relative speed between the substrate and pad, and the force pressing the substrate against the pad.
A reoccurring problem with fixed-abrasive pads is scratching of the substrate surface. Specifically, some CMP processes that use fixed-abrasive pads create shallow grooves, e.g., on the order of 500 angstroms deep, in the substrate surface. These grooves render the substrate finish unsuitable for integrated circuit fabrication, lowering the process yield.
In one aspect, the invention is directed to a method of polishing a substrate. The process includes chemical mechanical polishing the substrate with a fixed-abrasive polishing pad until it is substantially planarized, and chemical mechanical polishing the substrate with a non-fixed-abrasive polishing pad to remove any scratches.
Implementations of the invention may include the following. The fixed-abrasive polishing pad may be located at a first polishing station of a polishing apparatus, and the non-fixed-abrasive polishing pad may be located at a second polishing station of the polishing apparatus. The substrate may be chemical mechanical polished with a second fixed-abrasive polishing pad or a second non-fixed-abrasive polishing pad at a third polishing station, e.g., before polishing the substrate at the second polishing station. A first polishing liquid may be supplied to the first polishing station, a second polishing liquid may be supplied to the second polishing station, and a third polishing liquid may be supplied to the third polishing station. The first polishing liquid may have a different pH than the second polishing liquid. The second polishing liquid may contain abrasive particles. The fixed-abrasive polishing pad may include an upper layer that includes abrasive grains held in a binder material, and a lower layer selected from the group consisting of polymeric film, paper, cloth, and metallic film. The non-fixed-abrasive polishing pad may include a first layer including polyurethane and a second layer including compressed felt fibers, or a layer composed of a poromeric material.
In another aspect, the invention is directed to a method of forming a planarized layer on a substrate. A layer is formed on a non-planar surface of the substrate. The layer is chemical mechanical polished with a fixed-abrasive polishing pad until a residual layer remains over the surface, and the residual layer is chemical mechanical polished with a non-fixed-abrasive polishing pad to remove any scratches. The residual layer has a thickness equal to or greater than the depth of any scratches therein.
Implementations of the invention may include the following. The residual layer may have a thickness approximately equal to the depth of any scratches, e.g., about 100 to 1000 angstroms. Polishing with the non-fixed-abrasive polishing pad may cease when a layer having a target thickness, e.g., 300 to 1000 angstroms, remains over the non-planar surface.
Advantages of the invention may include the following. Scratching of the substrate is reduced or eliminated, thereby increasing process yield.
Other features and advantages will be apparent from the following description, including the drawings and claims.